Alloy articles for high temperature service



Patented July 4, 1950 ALLOY ARTICLES FOR HIGHTEWERATURE SERVICE RussellFranks and WilIiam QIBinQer, Niagara Falls, N. Y., assignors,byfln'iesne assignments, "-to Union Carbide and Carbon Corporation, a

' corporation of New York No Drawing. Application Mays, 194s,

Serial No. 668,328

This inventionrelates to alloy articles designed particularly for use inapplications where great strength "at very high temperatures isrequired.

The .contjinueddevelopment of such devices as superchargers, gas'turbines, jet propulsion apparatus and thelikedepends upon the production ofworkable metals-andpalloys that are strong at the high temper'aturesatwhich such devices operate. Although several alloys have been proposedforuse in high temperature applications, the utility of such alloys hasbe'enlimited either because they are (not hot-workable or machinable orbecause theybecomefbrittle upon continued exposure to elevatedtemperatures. One characteristic of highly alloyed ferrous metals whichcomplicates the problem considerably is that as the ferrous solidsolution is more heavily loaded with alloying materials to increase thehigh-temperature strength, thehighetemperature stability tends todecrease so that upon rolonged heating-the material. .becomes undulybrittle.

There. .is accordingly, a. need for hot-workable, machinable alloyarticles having great strength and stability at highly elevatedtemperatures, and it is the principal object of this invention tosatisfy this need.

This object is achieved by the present invention which comprises aferrous alloy containing chromium, nickel, cobalt, tungsten, and atleast one ;metal from the group consisting of columbi-um,tantalum,titanium, and vanadium, together with minor quantities ofmanganese, silicon, molybdenum, carbon, nitrogen. and impuritiescommonly-present in steels ofgood quality.

Specifically, the alloy of .theflpre'sent invention contains by weight15% to 25% chromium; 15% to 25% nickel; more than 25% but not more than45% cobalt; more than 7.5%,- preferably more than 10%-,'but .notmorethan 15% tungsteman aggregate of..0-5.%..t o 3% of one or. more of theelements columbium, tantalum, titanium, and vanadium; and u ,,.to.2%manganese, up to 1% si1icon,.up. to 0.35% carbon, 0.05 %,t 0.25% nitrogen; and theremaindersubstantially all iron and mc'identaljimpurities.Up toa'bout 3.5% molybdenum may bepresent, but addition molybdenumimparts no substantial benefit. The content of any single element of thecolumbium, tantalum. titanium, vanadium group should be less than 2%,and the titanium content should not exceed 1.5%. Somewhat more of theminor constituents than the upper limits just specified may on occasionbe used. For instance, if excellent forgeability is not essential, thecarbon content may be above 0.35%, up to say 1%. Iron is present in '3Claims. (Cl. 75-422) asubstantialproportion, the iron content being at'least 5 Alloys within the foregoing composition ranges arereadilyforged,'welcled, and machined 'and', as has been demonstratedby test,have remarkably great strength and stability 'athigh temperatures, forexample 1'200'F;"an'd upwards. Machine parts of the alloys may bedesigned "toioperate at high stress 'for'long periods of "time at 15001.and at lower stress for moderate periods at somewhat higher"temperatures. The invention includes" cast or hot-worked articlesandwelded articles for use at elevated temperatures "and composed ofsuch alloys.

A useful test for'determining the suitabilityof meta-Is and alloys forhigh temperature applications is the so-"called stress-rupture test; Inthis test, each 'ofseveral samples of atgiven material is' subjectedtoa'measured tensile stress at a particular elevated temperature, and thetime r'equired'for thesampleto' fail underthese. conditionsof'temperaturefand stress is'-'noted. The data obtained are thenplotted, using time and stress as abscissa and-ordinate respectively. Acurve is thus established 'for the material: tested, showing for theselected temperature the time requiredt'o causefailure of 'the' materialwhen a particular stress is applied. Usually curves are established forseveral different temperatures, and fromthese curves can be predictedquite accurately the length of time the material can Withstand failureat a givenstres's applied'at a given temperature. This 'info'rmati'on'isvaluable for design purposes, especially if the'material selected may besubjected to overheating, overloading, or both.

The alloy of theinven'tionhas beenshown'by stress-rupture tests to haveexcellent strength at high temperatures and the ability to withstandlarge stresses for prolonged periods'of time at high temperature.Forexample, in'one test a specimen of an alloy containing about 20%chromium; 20% nickel; 40% cobalt;'3% molybdenum; 12% tungsten; 1%columbium; 0.16% carbon; and 0;09% nitrogen, remaindersubstantially alliron withstood a stress of 20,000 pounds per square inch at atemperature of 1500 F. for 1485 hours before failure. This specimen hadbeen hot forged and then heated one hour at about v 2300" F. andquenched in water before testing.

The alloy of the invention may be forged or otherwise hot-worked withoutdifficulty in the range of 2100 F. to 1600 F. In some cases workingshould be continued to a temperature somewhat below therecrystallization temperature this invention is that it may be welded byordinary Welding methods including the various electric arc andoxyacetylene fusion-deposition methods, submerged-melt electric methodsand solid-phase pressure welding methods-thewelds produced being sound,tough, and ductile both in" the weld zone itself and in areasadjacentto'and remote from the weld zone.

To ensure the attainment of the desirable characteristics of the alloyof the invention it is most- 4 or more of the elements of the groupconsisting of columbium, tantalum, titanium and vanadium, the amount ofany single element of the lastnamed group being less than 2% of thealloy except the titanium content being not in excess of 1.5%; up to 2%manganese; up to 1% silicon; up to 0.35% carbon; 0.05% to 0.25%nitrogen;

' and the remainder iron and incidental impurities, the iron contentbeing at least 5%.

2. A heat resistant alloy article which in normal use is exposed toelevated temperatures of 1200 ments can not satisfactorily be ofiset byincreasing the proportions of cobalt and nickel in the alloy.Accordingly, care should be taken that the-composition limits describedbe observed in making the alloy.

If the alloy isintended for uses in which it will be exposed totemperatures not in excess of about 1350 F. compositions near the lowerlimits of the ranges given may be used, but if the alloy will be usedwhere exposure to temperatures above.

1350 Fjis probable, compositions near the upper limits of the rangesgiven should be employed. If the alloy is to be used where temperaturesnot in excess of 1200" F.wil1 be encountered, it may be used in the coldhot-worked condition, but where exposure to temperatures above 1200 F.is expected, the'alloy should be annealed'at a temperature of about2200F. to 2320 F. before use for best service.

Typical of articles for which the alloy of the invention 'is well suitedare blades; wheels and other parts of turbines. Such articles may beeither cast or wrought.

Although particular'emphasishas been laid on the hot working propertiesof the alloy of the invention and the use of the alloy for wroughtarticles, castings of the alloy also possess very useful properties athigh temperatures.

'We claim: Y

1. A heat resistant alloy article which innormal'use is exposed toelevated temperatures of 1200 F. and upwards and has great strength andstability when subjected to high'stresses at such elevated temperatures,said article being com- 3 posed of a machinable, weldable, hot-workableal- F. and upwards and has great strength when subjected tohighstressesat such elevated temperatures, said article being composed of ahot-workable alloy consisting of 15% to 25% chromium; 15% to 25% nickel;more than 25% but not more than 45% cobalt; at least 10% but not morethan 15% tungsten; up to 3.5% molybdenum; 0.5% to 3% in the aggregate ofone or more of the elements columbium, tantalum, titanium and vanadium,theamount of anysingle element of the last named group beingless than 2%of the alloy except the titanium content not exceeding 1.5%; manganesein an effective proportion up to 2%; silicon in an effective proportionup to 1%; carbon in an effective-proportion not exceeding 0.35%; 0.05%to 0.25% nitrogen; the remainder .ironand incidental impurities, theiron contentbeing atleast 5%.

3. A heat resistantalloy article which inner mal use may be exposed fora prolongedv period oftime to an elevated temperature ofthe order of1500 F. while subjected to high stressof the order of 20,000 ps. i. atsuch temperature for such period of time, said article having greatstrength under such conditions and composed of a hot-workable alloyconsisting substantially of 20% chromium; 20% nickel; 40%, cobalt; 3%molybdenum 12% tungsten; [1% columbium; 0.16% carbon; 0.09%,nitrogen;remainder iron.

vR SELL FRANKS.

WILLIAM 0. BINDER.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS- OTHER REFERENCES Kinzel and Franks: Alloys ofIronand Chromium, vol. II, 1940, pages 87, 88, 180,192, 194, 455',published by McGraw-Hill Book Co.,. N. Y.

Progress Report on NDRL Research Project, NRC8, P. B. 39, 578, October7, 1942, pages 1-21 inclusive (particularly page 5); Declassified toopen January 28, 1946.

1. A HEAT RESISTANT ALLOY ARTICLE WHICH IN NORMAL USE IS EXPOSED TOELEVAQTED TEMPERATURES OF 1200*F. AND UPWARDS AND HAS GREAT STRENGTH ANDSTABILITY WHEN SUBJECTED TO HIGH STRESSES AT SUCH ELEVATED TEMPERATURES,SAID ARTICLE BEING COMPOSED OF A MACHINABLE, WELDAVLE, HOT-WORKABLEALLOY CONTAINING: 15% TO 25% CHROMIUM; 15% TO 25% NICKEL; MORE THAN 25%BUT NOT MORE THAN 45% COBALT; AT LEAST 10% BUT NOT MORE THAN 15%TUNGSTEN; AN AGGREGATE OF 0.5% TO 3% OF ONE OR MORE OF THE ELEMENTSL OFTHE GROUP CONSISTING OF COLUMBIUM, TANTALUM, TITANIUM AND VANADIUM, THEAMOUNT OF ANY SINGLE ELEMENT OF THE LASTNAMED GROUP BEING LESS THAN 2%OF THE ALLOY EXCEPT THE TITANIUM CONTENT BEING NOT IN EXCESS OF 1.5%; UPTO 2% MAGNESE; UP TO 1% SILICON; UP TO 0.35% CARBON; 0.05% TO 0.25%NITROGEN; AND THE REMAINDER IRON AND INCIDENTAL IMPURITIES, THE IRONCONTENT BEING AT LEAST 5%.